Dissecting the maize genome by using chromosome addition and radiation hybrid lines

Abstract

We have developed from crosses of oat (Avena sativa L.) and maize (Zea mays L.) 50 fertile lines that are disomic additions of individual maize chromosomes 1-9 and chromosome 10 as a short-arm telosome. The whole chromosome 10 addition is available only in haploid oat background. Most of the maize chromosome disomic addition lines have regular transmission; however, chromosome 5 showed diminished paternal transmission, and chromosome 10 is transmitted to offspring only as a short-arm telosome. To further dissect the maize genome, we irradiated monosomic additions with gamma rays and recovered radiation hybrid (RH) lines providing low- to medium-resolution mapping for most of the maize chromosomes. For maize chromosome 1, mapping 45 simple-sequence repeat markers delineated 10 groups of RH plants reflecting different chromosome breaks. The present chromosome 1 RH panel dissects this chromosome into eight physical segments defined by the 10 groups of RH lines. Genomic in situ hybridization revealed the physical size of a distal region, which is represented by six of the eight physical segments, as being approximately 20% of the length of the short arm, representing approximately one-third of the genetic chromosome 1 map. The distal approximately 20% of the physical length of the long arm of maize chromosome 1 is represented by a single group of RH lines that spans >23% of the total genetic map. These oat-maize RH lines provide valuable tools for physical mapping of the complex highly duplicated maize genome and for unique studies of inter-specific gene interactions.

Fig. 1.

PCR products from DNA of the F₁ (Starter × B73) plant F₁-5133-1 when chromosome-specific SSR markers are used; electrophoresis in a 3.5% agarose gel shows the different elimination of maize chromosomes in individual tillers. Lanes 1, young plantlet; lanes 2, tiller F₁-5133-1/a; lanes 3, tiller F₁-5133-1/b; lanes 4, tiller F₁-5133-1/c; lanes 5, tiller F₁-5133-1/d; and lane M, standard 100-bp ladder.

Fig. 2.

Panel of the first RH lines for maize chromosome 1. Shown are the 15 SSR markers that frame the seven breakpoints, hence define the RH segments between p-umc1354 (most distal on the short arm) and p-umc2244 (most distal on the long arm) markers representing a genetic distance of more than 1,120 map units according to the IBM2 map.

Fig. 3.

GISH of metaphase chromosomes from root tips of three RH plants of the maize chromosome 1 panel. (A) Plant BC₁F₂, 1.07.3-001.3-3 (sibling of group 7), arrow points to the deficient short arm of maize chromosome 1; the chromosome lost ≈20% of its short arm. p-umc1626 is the most distal present marker tested (see also Fig. 2). The yellow-painted chromosome visualizes the segments 7 and 8 representing the genetic distance of 656-675 map units (B) Plant BC₁F₂ 1.07.2-007.3-4 (sibling of group 9), arrow points to the translocation fragment visualizing the RH segment 8. The translocation fragment accounts for ≈20% of the long-arm length representing the genetic distance of 261-332 map units (C) Plant BC₁F₂ 1.07.1-020.3-1 (sibling of group 3), arrow points to the translocation fragment visualizing the RH segments 1 and 2 accounting for ≈15% of the short-arm length representing the distance of 226-257 map units.